Make payment manifest download/parse cross-platform

components/payments/content/payment_manifest_parser.mojom

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 [JavaPackage="org.chromium.payments.mojom"]
 module payments.mojom;
 
 struct PaymentManifestSection {
   string package_name;
   // Optional version number. 0 if not defined.
   int64 version;
   // The result of SHA256(signing certificate bytes) for each certificate in the
   // package.
   array<array<uint8, 32>> sha256_cert_fingerprints;
 };
 
 interface PaymentManifestParser {
   Parse(string content) => (array<PaymentManifestSection> manifest);
 };